Evaluation of the Inter-Chain Free Space in Rubbery and Glassy cis-Polyisoprene by a Molecular Simulation

Abstract

The free space in melt, rubbery, and glassy cis-polyisoprene (cis-PI) has been investigated by inserting hypothetical sphere molecules of various sizes. The polymer structures at various temperatures were created by molecular dynamic simulations. The accessible volume was calculated by counting the subcells in which hypothetical sphere from σ=3.0A to 6.0A (σ means the atom size in Lennard-Jones (12, 6) potential) can be successfully inserted into the systems. The accessible volume is randomly located for the various sizes of the clusters in the system. The number of the clusters and the volume fraction of the clusters with the particular size were analyzed. In low ternperature rubber (273 K), the accessible volumes seemed to be isotropically shrunk when compared with the volumes in the melt state (373 K). In contrast, at glassy state (173 K) some of the accessible volumes which accommodate the spheres from σ=3.0A to 5.0A in rubbery state are frozen near the glass transition (273 K), resulting in the existence of the unrelaxed volume.